ASTRO Spectra receive question

[asmitty0010]

Our angency has an astro spectra that doesn't receive as well as it should. We've sent it in for tuning and the radio shop said it was as good as it was going to get. If i purchase a NOS RF board would that increase that fix this?

Again we have multiple astros and we've tried them on the same antenna but one of ours acts like something is gone on the receiving end. It will only receive if the signal is right on top of the unit so to speak.

thanks

[Bill_G]

I don't know what a NOS RF board is. It sounds like further troubleshooting is required. I have limited ASTRO Spectra experience, but Spectra rcvrs in general don't develope poor receive problems except two ways:

the contacts in the antenna port are spread and do not mate well with your antenna line, but do with the radio shop cable

the rcvr RF board has failed (maybe this is the board you were talking about)

I'd have the shop look at it one more time.

[motorola_otaku]

NOS = New Old Stock; i.e. old stock of a discontinued part.

Three questions: what band and sub-range (if VHF/UHF) is the radio, are you using it in analog or P25, and are you trying to go out-of-band with it? Measured RX sensitivity for an Astro Spectra should be on par with their analog predecessors: .21 to .3 microvolts. Actual specified RX sensitivity is .3 with preamp and .5 without (I have never seen one without a preamp.. maybe yours is one)for VHF and UHF at 20 dB quieting and .35 at 12dB SINAD for 800.

There aren't any alignment settings for the Astro Spectra that would affect RX sensitivity. Honestly, I've never had one go deaf or even partially deaf unless I was trying to go out of band with it, even during codeplug fenagling. I guess as good a place to start as any would be putting it on a service monitor and seeing what it's actually doing (checking TX power wouldn't be a bad idea either, even if its intended use is RX-only), then popping the lids and checking to make sure all of the cables are properly seated, then swapping the receive preselector out with one from an identical range radio (the donor can be an analog Spectra, too.)

[asmitty0010]

Well found out some interesting news today. Our radio tech we talked to today thinks that a transmitting radio was too close to the receiving antenna and caused something to blow on the astro unit.

Any ideas how to fix this?

[Will]

This is a common problem especially on the High power Astros. High VSWR burns out the receiver frontend.
A simple check with a voltmeter will show if the RF front end is working properly.

I have no problem repairing them here. In fact I have some newer transistors that work better.

[jhansen27]

I just unfortunately suffered this same condition with my VHF Astro Spectra (high power). Not sure if it was the adjacent VHF (2m HAM @50w) or otherwise. Any suggestion on replacement parts to "beef up" the front end of this radio and prevent another failure? I am also unfortunately lacking a service manual for this, so I may be forced to send somewhere for repair (I'm open if someone has suggestions).

Jeremy

[kt2728]

This is a common problem especially on the High power Astros. High VSWR burns out the receiver frontend.
A simple check with a voltmeter will show if the RF front end is working properly.

I have no problem repairing them here. In fact I have some newer transistors that work better.

can this be caused by the diodes in the antenna switch too? i was thinking that was the problem when you fixed one of those radios for me.

kt

[Will]

This is a common problem especially on the High power Astros. High VSWR burns out the receiver frontend.
A simple check with a voltmeter will show if the RF front end is working properly.

I have no problem repairing them here. In fact I have some newer transistors that work better.

can this be caused by the diodes in the antenna switch too? i was thinking that was the problem when you fixed one of those radios for me.

kt

KT,

Yes I replaced the RF amp and one of the antenna switches.

[kt2728]

There you have it, if you can't get your local mss to fix it send it to will.

[jhansen27]

Update: Simple fix. Replaced T/R switch (diode which shorts RX to GND when PTT is active). This was a very simple fix. I am told that there is an upgraded replacement component which is less susceptible to failure, can anyone share?

Jeremy